The electrical components used in a control system are, depending on their type, partially or wholly non-resistant to pressure. The housing chamber containing the electrical equipment must, therefore, be able to breathe. In other words, no pressure higher or lower than atmospheric pressure may build up in the housing chamber, i.e., the housing chamber should be able to breathe. In this context it is immaterial whether the pressure originates in a terrestrial atmosphere or in an artificial atmosphere, e.g., a protective gas.
It is known to effect the breathing of the housing chamber via its own breathing device. This breathing device permits flow out of the housing chamber into the atmosphere, as well as in the opposite direction. An additional goal of the breathing device is to inhibit the penetration of pollutants and humidity into the housing chamber from the atmosphere. This goal is not attained to a satisfactory extent in all cases. Consequently, disturbances in operation may occur.